An adhesive label commonly called a label or label sticker is widely used in a variety of industries including trademarks and advertising of products as well as printing, chemicals, medicine, home appliances, automobiles and writing supplies. A material to which an adhesive label is adhered may be any natural or synthetic material. The surface paper generally used for adhesive labels is paper such as art paper or vellum paper, or a film such as PET, PVC, PE or PP. The surface is subjected to a predetermined printing process and is thus applied to final products.
The adhesive strength of the adhesive to be coated on the surface of paper may be determined depending on the intended purpose. A permanent adhesive typically has a high adhesive strength of 800 to 1,000 g/in. Paper used as surface paper is torn off when the permanent adhesive is removed. Meanwhile, when a removable adhesive is temporally used for labeling, the removable adhesive should exhibit low adhesive strength, allowing removal, and not be transferred to the material to which the adhesive has been attached.
In order to secure such removability, control of components, cross-linkage density and suitable molecular structures (such as molecular weight and molecular weight distribution) of the adhesive is required. In particular, suitable control of a cross-linking agent is known to enable removability of the adhesive to be controlled.
U.S. Pat. No. 6,586,510 discloses an acrylic adhesive with controlled removability using cross-linking monomers having a variety of functional groups such as allyl methacrylate, diallyl malate or ethylene glycol diacrylate.
In addition, US Patent Publication No. 2004/0116598 discloses an adhesive with superior removability and water-resistance, obtained by applying an aziridine cross-linking agent to an adhesive resin.
Meanwhile, a plasticizer is used to impart workability and flexibility to the adhesive and contribute to reduction of noise generated during removal of the adhesive. US Patent Publication No. 2008/0090948 discloses a combination of a wax such as a polypropylene wax, a polyethylene wax, PTFE or a paraffin wax, and a silicone resin to realize low noise.
However, a plasticizer generally moves to the surface and further involves contamination of the material to which the adhesive is attached. Accordingly, selection of the plasticizer should be made under careful consideration.
Korean Patent Laid-open No. 2009-0033423 discloses an adhesive sheet for optical applications using an acetyl tributyl citrate plasticizer to solve removability and contamination of the material to which the adhesive is attached. U.S. Pat. No. 6,586,510 discloses a removable adhesive comprising 5% or less of a wax and 5 to 12.5% of a triethyl citrate plasticizer. However, these related arts disadvantageously do not satisfy all requirements of superior removability and heat resistance, low release noise and absence of residues.